PROBLEM TO BE SOLVED: To provide a system and a method for tagging a document for the purpose of preventing forgery. SOLUTION: In the system and method for determining the origin and the originality by tagging a recording sheet, a roller 10 for transferring at least a part of a random pattern 11 to a document is provided. The random pattern 11 is transferred to the sheet by press, die floating or punching. The pattern 11 being transferred to the sheet can be determined by a known technology and these patterns 11 can be imaged and stored in a data base. When a plurality of rollers 10, 20 are employed in series, the random pattern 11 can be transferred to one side or both sides of the sheet while varying the phase. A sequence code can be established by determining the phase difference of the random pattern 11. The rollers 10, 20 (including a plurality of rollers) provided with the random pattern 11 can be fixed to an imaging apparatus, especially the sheet carrying mechanism thereof.

Cryptography is a powerful tool for building secure distributed systems, albeit at substantial computational cost. This is especially true for public key cryptography. Conventional wisdom dictates that cryptography must be done locally in order to be secure. We argue for an approach in which public key cryptographic operations are provided as a network service. This service operates over longlived associations secured by symmetric cryptography. This network architecture amortizes the cost of specialpurpose cryptographic hardware across many users. We describe the implementation of such a system, and performance results we obtained.